High-voltage transistors are a foundational element of numerous applications. For instance, such transistors are frequently used in constructing circuitry such as input/output (IO) circuitry, electrostatic discharge protection circuitry, clamps, and other off-chip interfaces of system-on-chip (SoC) configurations. An example high-voltage transistor device is the vertical drain metal oxide semiconductor (VDMOS) transistor. In a VDMOS transistor, the drain is separated from the gate through the use of shallow-trench isolation. As high-voltage is applied to the drain, the voltage is reduced before reaching the intrinsic gate, enabling higher voltage operation. There are a number of non-trivial challenges with this integration scheme.
As will be appreciated, the figures are not necessarily drawn to scale or intended to limit the disclosure to the specific configurations shown. For instance, while some figures generally indicate straight lines, right angles, and smooth surfaces, an actual implementation of a structure may have less than perfect straight lines, right angles, and some features may have surface topology or otherwise be non-smooth, given real world limitations of the processing equipment and techniques used. In short, the figures are provided merely to show example structures.